The present invention relates to a process for the preparation of polyaryl ether ketones by electrophilic polycondensation using acyl halides as a monomer component in the presence of a Lewis acid.
Polyaryl ether ketones, in particular all para-bonded polyaryl ether ketones, have a large number of interesting properties, for example processability by thermoplastic methods, high-temperature stability, mechanical stability and excellent resistance to chemicals.
The literature describes two synthesis methods for the preparation of polyaryl ether ketones. In the case of the nucleophilic procedure, ether bonds are established between hydroxyaromatics and aromatics activated with respect to nucleophilic aromatic substitution.
In the case of the electrophilic procedure, generally aromatic dicarboxylic acid derivatives or phosgene are reacted with suitable aromatic compounds which contain two hydrogen atoms capable of electrophilic substitution, with formation of a diaryl ketone linkage, or an aromatic carboxylic acid derivative which contains both an acid derivative group and a substitutable hydrogen atom is subjected to autopolycondensation. U.S. Pat No. 3,441,538, U.S. Pat. No. 3,442,857, U.S. Pat. No. 953,400, DE-A 32 41 444, DE-A 34 16 445 and DE-A 34 16 446 describe electrophilic polycondensation reactions in which HF is used as a solvent and BF.sub.3 as a catalyst. Alternatively, halogenated hydrocarbons may also be used as solvents, in combination with other Lewis acids, in particular AlCl.sub.3, as a catalyst.
In these cases, it has proven advantageous to carry out the reaction in the presence of a Lewis base to be used in more than stochiometric amounts, in order to reduce the activity of the Lewis acid and hence to steer the substitution of the electron-rich aromatic by the acyl chloride selectively to the para position. Undesirable secondary reactions with the solvent or ortho substitutions of the electron-rich aromatic by the acyl chloride can thus be substantially suppressed (WO 84/03891 and WO 84/03892). The suppression of secondary reactions, for example the alkylation of the polyaryl ether ketones by the solvent or the ortho-acylation Of activated aryloxy groups, leads to an industrially usable molecular weight and sufficient melt stability of the polymers and permits the processing of the products by extrusion or injection molding.
A feature common to all electrophilic polycondensation processes is the working up of the products by hydrolysis, the polyaryl ether ketone/Lewis acid complex formed as an intermediate being destroyed. This working up by hydrolysis gives large amounts of aqueous solutions of Lewis acid catalysts, in particular aluminum chloride, which lead to pollution of waste water. In particular, the use of Lewis bases as a moderator in the polycondensation causes a significantly higher consumption of Lewis acid catalyst since some of the Lewis acid catalyst is deactivated by complex formation with the Lewis base. According to U.S. Pat. No. 4,709,007, a further equivalent of catalyst is required per equivalent of Lewis base used, the amount of Lewis base usually used being preferably 0.5 equivalent, based on the carbonyl groups present in the polymer. This leads to an increase in the pollution of the waste water by residual amounts of Lewis base and by hydrolysis products of the Friedel-Crafts catalyst.
It is an object of the present invention to provide a process for the preparation of polyaryl ether ketones by electrophilic polycondensation which does not have the disadvantages described above but in which high molecular weight, crystalline polyaryl ether ketones having good melt stability can nevertheless be prepared.